JP2010101940A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device that obtains a high quality image, free from development history (ghost) for a long period of time by using a hybrid development system provided with a plurality of developer carriers, thereby maintaining the ability of each developer carrier to recover toner, and to provide an image forming apparatus. <P>SOLUTION: The surface of each developer carrier for recovering toner is composed of a material that is conductive and that removes electricity from toner by contact-charging toner adhering to the surface. Accordingly, by removing electricity from toner stuck to the surface of the developer carrier for toner recovery, degradation in the ability to recover toner, which is caused by an accumulation of toner, is suppressed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention uses a developer containing a carrier and toner, and supplies a toner carrier for supplying toner to the toner carrier, and a toner carrier for developing a latent image with the supplied toner. The present invention relates to a hybrid developing device provided with a toner collecting developer carrying member for collecting undeveloped toner from a toner carrying member, and an image forming apparatus using the same.

  Conventionally, as a developing method in an image forming apparatus using an electrophotographic method, a one-component developing method using only toner as a developer and a two-component developing method using toner and a carrier are known.

  The one-component development system is advantageous in terms of simplification, miniaturization, and cost reduction of the apparatus, but the deterioration of the toner is likely to be accelerated by the strong stress of the regulating part that charges the toner, and the charge acceptability of the toner is reduced. It's easy to do. Further, the toner regulating member and the surface of the toner carrying member are contaminated with the toner and the external additive, so that the charge imparting property to the toner is also lowered, and as a result, the life of the developing device is shortened.

  In the two-component development system, the toner is charged by frictional charging by mixing with the carrier, so that the stress is small and it is advantageous for the deterioration of the toner. Furthermore, since the surface area of the carrier is large, it is relatively strong against contamination by toner and external additives, which is advantageous for extending the life.

  However, in the two-component development method, when developing the electrostatic latent image on the image carrier, the surface of the image carrier is rubbed with the magnetic brush of the developer, so that a magnetic brush mark may be generated. Furthermore, there is a problem that the carrier easily adheres to the image carrier and causes an image defect.

  As a development method that solves the problem of image defects while having the long-life characteristics of the two-component development method, the two-component developer is supported on the developer carrier, and only the toner from the two-component developer is changed to the toner carrier. A so-called hybrid development system that is supplied and used for development is disclosed (see Patent Document 1).

  However, the hybrid development system has a problem that undeveloped toner that has not been used for development on the toner carrier appears on the image as a development history (ghost) in the next development process. This is because priority is given to supplying a toner necessary for development to the toner carrying member by applying a bias to the developer carrying member, and thus the developer carrying member does not have sufficient ability to collect the development residual toner. is doing.

  In recent years, in order to solve this problem, there has been proposed a method in which a developer collecting member for collecting toner is added and a voltage for collecting the development residual toner on the toner carrying member is applied in the hybrid developing method (see Patent Document 2). ). According to the technique described in Patent Document 2, the development residual toner on the toner carrying member can be reliably collected by the toner collecting developer carrying member, so that the problem of development history (ghost) does not occur in the initial stage.

  However, in this method, since the voltage for attracting the toner is always applied in the direction of the toner collecting developer carrier, the toner in the developer is separated from the carrier, and the toner moves to the surface of the toner collecting developer carrier. In addition, uneven distribution of toner occurs.

  When the toner is unevenly distributed on the surface of the toner collecting developer carrier, the unevenly distributed toner remains on the surface of the toner collecting developer carrier when the developer is removed from the toner collecting developer carrier. To do. As a result, the toner is accumulated on the developer carrying member for collecting the toner by repeated use.

Accumulation of charged toner obstructs the recovery electric field in the toner recovery area and lowers the toner recovery capability. For this reason, the recovery capability that was initially sufficient does not last for a long period of time, and ghosting becomes a problem as image formation is repeated.
JP-A-5-150636 JP-A-10-319708

  As described above, technical improvements have been made to cope with ghosting in the hybrid development method, but no technology that sufficiently satisfies the requirements has been proposed.

  Accordingly, an object of the present invention is to solve the above-mentioned problems and to maintain a toner recovery capability using a hybrid development system provided with a plurality of developer carriers, and to produce a high-quality image free from development history (ghost). It is an object to provide a developing device and an image forming apparatus that can be obtained over a long period of time.

  In order to solve the above problems, the present invention has the following characteristics.

  1. A developer tank containing a developer including toner and a carrier; a toner supply developer carrier that receives and supplies the developer from the developer tank; and a toner supply developer carrier. A toner carrier that carries and transports the toner supplied and develops the latent image on the image carrier, and a developer for toner collection that carries and transports the developer and collects residual toner from the toner carrier. A toner collecting developer carrier, the surface of which has conductivity, and the charge is removed by contact charging with the toner adhering to the surface. A developing device comprising the above material.

  2. The toner collecting developer carrying member is rotatable in the circumferential direction, has a conductive surface, and a sleeve roller having a coating layer made of a material that neutralizes toner by contact charging, and the sleeve roller. 2. The developing device according to 1, wherein the developing device includes a magnet body contained therein.

  3. 3. The developing device according to claim 1, further comprising a developer disturbing member that contacts the developer collecting member for collecting toner through a developer layer collected with toner on the developer collecting member for collecting toner. .

  4). 4. The developing device according to 3, wherein at least the surface of the developer disturbing member has conductivity.

  5. 5. The developing device according to claim 4, wherein a bias voltage is applied between the developer disturbing member and the toner collecting developer carrier so as to attract the toner toward the developer disturbing member. .

  6). 6. The developing device according to claim 3, wherein the developer disturbing member has a surface made of a material that neutralizes toner by contact charging.

  7). An image bearing member and a developing device that develops a latent image formed on the surface of the image bearing member to form a toner image, wherein the developing device is the developing device according to any one of 1 to 6. An image forming apparatus.

  According to the present invention, it is possible to reliably collect the development residual toner on the toner carrier by the developer carrier for toner collection, and to neutralize the collected toner by contact with the surface of the developer carrier for toner collection. Accumulation of toner on the surface of the developer carrying member for collecting toner can be avoided.

  Accordingly, it is possible to provide a developing device and an image forming apparatus that can obtain a high-quality image that maintains the toner recovery capability and does not cause a ghost problem over a long period of time.

(First embodiment)
A first embodiment of the present invention will be described below with reference to the drawings.

(Configuration and operation of image forming apparatus)
FIG. 1 shows a configuration example of a main part of the image forming apparatus according to the first embodiment of the present invention. The schematic configuration and operation of the image forming apparatus according to the first embodiment will be described with reference to FIG.

  The image forming apparatus is a printer that performs image formation by transferring a toner image formed on an image carrier (photosensitive member) 1 to a transfer medium P such as paper by an electrophotographic method.

  The image forming apparatus includes an image carrier 1 for carrying an image. Around the image carrier 1, a charging member 3 for charging the image carrier 1 and an image carrier 1 are provided. A developing device 2 a for developing an electrostatic latent image, a transfer roller 4 for transferring a toner image on the image carrier 1, and a cleaning blade 5 for removing residual toner on the image carrier 1 are provided on the image carrier 1. They are arranged in order along the rotation direction A.

  The image carrier 1 is charged by the charging member 3 and then exposed by an exposure device 30 equipped with a laser emitter or the like at the point E in the figure, and an electrostatic latent image is formed on the surface thereof. . The developing device 2a develops the electrostatic latent image to form a toner image. The transfer roller 4 transfers the toner image on the image carrier 1 to the transfer medium P, and then discharges it in the direction of arrow C in the figure. The cleaning blade 5 removes the residual toner on the image carrier 1 after the transfer with a mechanical force.

  For the image carrier 1, the charging member 3, the exposure device 30, the transfer roller 4, the cleaning blade 5 and the like used in the image forming apparatus, a well-known electrophotographic technique may be arbitrarily used. For example, although a charging roller is shown as the charging member 3 in the figure, a charging device that is not in contact with the image carrier 1 may be used. Further, for example, there may be no cleaning blade.

  Next, a configuration example of the developing device 2a of the hybrid developing system according to the present embodiment will be described.

  The developing device 2a includes the following components. That is, a developer tank 16 that contains a developer 24 containing toner and a carrier, a toner supply developer carrier 11 that carries and conveys the developer 24 supplied from the developer tank 16 on the surface, and a toner supply development. The toner carrier 25 receives only the toner from the agent carrier 11 in the toner supply region 7 and develops the electrostatic latent image formed on the image carrier 1. After passing through the developing region 6, the toner carrier 25. A toner collecting developer carrier 26 for collecting the development residual toner remaining on the toner collecting area 8 is provided.

  The developing device 2a also includes a toner carrier bias power source 31 that supplies a voltage to the toner carrier 25, a toner carrier bias power source 32 that supplies a voltage to the toner supply developer carrier 11, and a toner recovery unit. A developer collecting member bias power source 33 for supplying a voltage to the developing agent carrier 26.

  The detailed configuration and operation of the developing device 2a will be described later.

(Developer composition)
The configuration of the developer used in the developing device according to this embodiment will be described.

  The developer 24 used in the present embodiment includes toner and a carrier for charging the toner.

<Toner>
The toner is not particularly limited, and a known toner that is generally used can be used, and a colorant, a charge control agent, a release agent, and the like are contained in the binder resin, and external additives are added. What processed the agent can be used. The toner particle diameter is not limited to this, but is preferably about 3 to 15 μm.

  In producing such a toner, it can be produced by a publicly known method. For example, it can be produced using a pulverization method, an emulsion polymerization method, a suspension polymerization method or the like.

  The binder resin used in the toner is not limited to this. For example, styrene resin (monopolymer or copolymer containing styrene or a styrene-substituted product), polyester resin, epoxy resin, vinyl chloride Resins, phenol resins, polyethylene resins, polypropylene resins, polyurethane resins, silicone resins and the like can be mentioned. It is preferable to use those having a softening temperature in the range of 80 to 160 ° C. and those having a glass transition point in the range of 50 to 75 ° C., depending on the resin alone or the composite.

  Further, as the colorant, known ones that are generally used can be used. For example, carbon black, aniline black, activated carbon, magnetite, benzine yellow, permanent yellow, naphthol yellow, phthalocyanine blue, first sky blue, ultra Marine blue, rose bengal, lake red and the like can be used, and it is generally preferable to use them in a proportion of 2 to 20% by mass with respect to the binder resin.

  As the charge control agent, known ones can be used. Examples of the charge control agent for positively chargeable toners include nigrosine dyes, quaternary ammonium salt compounds, triphenylmethane compounds, imidazoles. System compounds and polyamine resins. Examples of charge control agents for negatively chargeable toners include metal-containing azo dyes such as Cr, Co, Al, and Fe, salicylic acid metal compounds, alkylsalicylic acid metal compounds, and calixarene compounds. In general, the charge control agent is preferably used in a proportion of 0.1 to 10% by mass with respect to the binder resin.

  In addition, as the above-mentioned mold release agent, known ones that are generally used can be used. For example, polyethylene, polypropylene, carnauba wax, sazol wax and the like can be used alone or in combination of two or more. In general, it is preferably used at a ratio of 0.1 to 10% by mass with respect to the binder resin.

  Also, as the above external additives, publicly known publicly known materials can be used. For example, inorganic fine particles such as silica, titanium oxide, aluminum oxide, acrylic resin, styrene resin, silicone resin, fluorine resin Resin fine particles such as silane coupling agent, titanium coupling agent, and silicone oil are preferably used. Such a fluidizing agent is added to the toner at a ratio of 0.1 to 5% by mass and used. The number average primary particle size of the external additive is preferably 10 to 100 nm.

  Further, as the external additive, reverse polarity particles having a chargeability opposite to that of the toner may be used. The reverse polarity particles preferably used are appropriately selected depending on the charging polarity of the toner.

  When a negatively chargeable toner is used as the toner, fine particles having positive chargeability are used as the opposite polarity particles. For example, inorganic fine particles such as strontium titanate, barium titanate, and alumina, acrylic resin, benzoguanamine resin, nylon ( Fine particles made of thermoplastic resin such as (registered trademark) resin, polyimide resin, polyamide resin or thermosetting resin can be used. Further, a positive charge control agent imparting positive chargeability may be contained in the resin, or a copolymer of nitrogen-containing monomers may be constituted.

  As the positive charge control agent, for example, nigrosine dye, quaternary ammonium salt and the like can be used, and as the nitrogen-containing monomer, 2-dimethylaminoethyl acrylate, 2-diethylaminoethyl acrylate, 2-Dimethylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, vinylpyridine, N-vinylcarbazole, vinylimidazole and the like can be used.

  On the other hand, in the case of using a positively chargeable toner, fine particles having negative chargeability are used as the reverse polarity particles. For example, in addition to inorganic fine particles such as silica and titanium oxide, fluorine resin, polyolefin resin, silicone resin, polyester resin Fine particles composed of a thermoplastic resin such as a thermosetting resin or the like can be used. Further, a negative charge control agent imparting negative chargeability may be contained in the resin, or a copolymer of a fluorine-containing acrylic monomer or a fluorine-containing methacrylic monomer may be constituted. Examples of the negative charge control agent include salicylic acid-based and naphthol-based chromium complexes, aluminum complexes, iron complexes, and zinc complexes.

  In addition, in order to control the chargeability and hydrophobicity of the reverse polarity particles, the surface of the inorganic fine particles may be surface treated with a silane coupling agent, a titanium coupling agent, silicone oil, etc. When imparting positive chargeability, surface treatment with an amino group-containing coupling agent is preferred, and when imparting negative chargeability, surface treatment with a fluorine group-containing coupling agent is preferred.

  The number average particle diameter of the reverse polarity particles is preferably 100 to 1000 nm. It is used by adding 0.1 to 10% by mass with respect to the toner.

<Carrier>
The carrier is not particularly limited, and a commonly used carrier can be used, and a binder type carrier, a coat type carrier, and the like can be used. The carrier particle size is not limited to this, but is preferably 15 to 100 μm.

  The binder type carrier is obtained by dispersing magnetic fine particles in a binder resin, and positive or negative chargeable fine particles can be fixed to the carrier surface or a surface coating layer can be provided. The charging characteristics such as the polarity of the binder type carrier can be controlled by the material of the binder resin, the chargeable fine particles, and the type of the surface coating layer.

  Examples of the binder resin used in the binder-type carrier include thermoplastic resins such as vinyl resins, polyester resins, nylon resins, polyolefin resins, and the like typified by polystyrene resins, and curable resins such as phenol resins. .

  Magnetic fine particles of the binder type carrier include spinel ferrite such as magnetite and gamma iron oxide, and magnets such as spinel ferrite and barium ferrite containing one or more metals other than iron (Mn, Ni, Mg, Cu, etc.). Plumbite type ferrite, iron or alloy particles having an oxide layer on the surface can be used. The shape may be granular, spherical, or needle-shaped. In particular, when high magnetization is required, it is preferable to use iron-based ferromagnetic fine particles. In consideration of chemical stability, it is preferable to use ferromagnetic fine particles of magnetoplumbite type ferrite such as spinel ferrite and barium ferrite containing magnetite and gamma iron oxide. A magnetic resin carrier having a desired magnetization can be obtained by appropriately selecting the type and content of the ferromagnetic fine particles. The magnetic fine particles are suitably added to the magnetic resin carrier in an amount of 50 to 90% by mass.

  Silicone resin, acrylic resin, epoxy resin, fluorine resin, etc. are used as the surface coating material of the binder type carrier, and these resins are coated on the surface and cured to form a coating layer, thereby providing a charge imparting ability. Can be improved.

  For example, the charging fine particles or the conductive fine particles are fixed to the surface of the binder type carrier by, for example, mixing the magnetic resin carrier and the fine particles uniformly, adhering these fine particles to the surface of the magnetic resin carrier, and then mechanically and thermally. By applying a strong impact force and fixing the fine particles so as to be driven into the magnetic resin carrier. In this case, the fine particles are not completely embedded in the magnetic resin carrier, but are fixed so that a part thereof protrudes from the surface of the magnetic resin carrier.

  As the chargeable fine particles, organic or inorganic insulating materials are used. Specifically, organic insulating fine particles such as polystyrene, styrene copolymer, acrylic resin, various acrylic copolymers, nylon, polyethylene, polypropylene, fluororesin, and cross-linked products thereof may be used as the organic type. Regarding the charge level and polarity, a desired level of charge and polarity can be obtained by a material, a polymerization catalyst, surface treatment, and the like. Further, as the inorganic type, negatively charged inorganic fine particles such as silica and titanium dioxide, and positively charged inorganic fine particles such as strontium titanate and alumina are used.

  On the other hand, a coated carrier is a carrier in which a carrier core particle made of a magnetic material is coated with a resin, and in a coated carrier, positive or negatively chargeable fine particles are fixed on the surface of the carrier as in a binder type carrier. it can. Charging characteristics such as polarity of the coat type carrier can be controlled by the type of the surface coating layer and the chargeable fine particles, and the same material as the binder type carrier can be used. In particular, the coating resin can be the same resin as the binder resin of the binder type carrier.

  The mixing ratio of the toner and the carrier may be adjusted so as to obtain a desired toner charge amount. The mixing ratio of the toner is 3 to 50% by mass, preferably 6 to 30% by mass with respect to the total amount of the toner and the carrier. Is suitable.

(Configuration and operation of developing device 2a)
A detailed configuration example and operation example of the developing device 2a according to the present embodiment will be described with reference to FIG.

<Device configuration>
The developer 24 used in the developing device 2a is composed of toner and carrier as described above, and is stored in the developer tank 16.

  The developer tank 16 is formed by a casing 19 and normally contains mixing and agitating members 17 and 18 therein. The mixing stirring members 17 and 18 mix and stir the developer 24 and supply the developer 24 to the toner supply developer carrier 11. An ATDC (Automatic Toner Density Control) sensor 20 for detecting the toner concentration is preferably disposed at a position of the casing 19 facing the mixing and agitating member 18.

  The developing device 2 a normally has a replenishing unit 10 for replenishing the developer tank 16 with the toner consumed in the developing area 6. In the replenishing unit 10, the replenishing toner 23 sent from a hopper (not shown) containing the replenishing toner 23 is replenished into the developer tank 16. The replenishment operation may be controlled based on the output of the ATDC sensor 20.

  The developing device 2 a also includes a regulating member (regulating blade) 15 for thinning the developer for regulating the amount of developer on the toner supply developer carrier 11.

  The toner supply developer carrier 11 is generally composed of a magnet body 13 that is fixedly arranged and a rotatable sleeve roller 12 that encloses the magnet body 13, and supplies toner to the toner carrier 25 during image formation. The toner supply bias is applied by the toner supply developer carrier bias power source 32.

  The magnet body 13 has five magnetic poles N1, S1, N2, N3, and S2 along the rotation direction of the sleeve roller 12. Of these magnetic poles, the main magnetic pole N <b> 1 is disposed at the position of the toner supply region 7 facing the toner carrier 25.

  Similarly, the toner collecting developer carrier 26 is composed of a magnet body 28 that is fixedly arranged and a rotatable sleeve roller 27 that encloses the magnet body 28, and for collecting the development residual toner on the toner carrier 25. The collection bias is applied by a bias power supply 33 for a developer carrying member for collecting toner.

  The magnet body 28 has five magnetic poles N4, S3, N5, S4, and N6 along the rotation direction of the sleeve roller 27. Of these magnetic poles, the main magnetic pole S <b> 3 is disposed at the position of the toner recovery area 8 facing the toner carrier 25.

  Further, homopolar portions N6 and N4 that generate a repulsive magnetic field for peeling off the developer 24 on the sleeve roller 27 are arranged at positions facing the inside of the developer tank 16.

  Further, in the developing device 2a, in order to transfer the developer 24 on the toner supply developer carrier 11 to the toner collection developer carrier 26, each of the S1 pole and the N4 pole serves as a toner supply developer. The carrier 11 and the developer collecting member 26 for collecting toner are arranged at the opposing portions. The developer 24 is delivered and transported from the S1 magnetic pole side of the toner supply developer carrier 11 to the N4 magnetic pole side of the toner collection developer carrier 26.

<Developer carrier structure>
The configuration of the toner collecting developer carrier 26 will be further described.

  At least the surface (the surface of the sleeve roller 27) of the toner collecting developer carrier 26 is made of a charge eliminating material 41 that has conductivity and has a polarity that removes the toner on the charging series.

  The neutralizing material 41 having such a polarity as to neutralize the toner is a material having a more negative polarity than the toner in the charging series when the normal charging polarity of the toner is negative, and when the normal charging polarity of the toner is positive. It is a material having a more positive polarity than the toner in the charging series. As a result, the toner can be removed by contact with the toner.

In addition, the charge-removing material 41 having conductivity means that the charge delivered when the toner is discharged is rapidly attenuated and has a low resistance so that charge-up due to surface electrification does not occur. Although it depends on the thickness of the resistance layer, it indicates a material having a resistance lower than about 10 ⁹ Ω · cm.

  Such a charge removal material 41 can be produced by dispersing a low-resistance material in a charged polarity material for discharging the toner. If the electrified material that removes the selected toner has its own conductivity, it is not necessary to disperse the low-resistance material. Since many of these materials are insulating materials, examples in which conductivity is imparted by dispersing low resistance materials are listed below. However, this does not matter as long as the above requirements are satisfied.

  As an example of a material having a charging polarity for discharging the toner, for example, when the normal charging polarity of the toner is negative, a fluorine-based resin such as tetrafluoroethylene resin can be exemplified, and the normal charging polarity of the toner is positive. In this case, examples include polyamide (nylon) and silicon resin. Examples of the low resistance material dispersed in these materials include carbon and various conductive metal particles.

  By applying the static eliminating material 41 as described above to the surface of the sleeve roller 27, a desired toner collecting developer carrier 26 can be obtained. The reason why such a charge eliminating material 41 is used on the surface of the toner collecting developer carrier 26 is to avoid the accumulation of unevenly distributed toner on the surface of the toner collecting developer carrier 26. Accumulation of unevenly distributed toner and a mechanism for avoiding this will be described later.

  Further, by appropriately adjusting the conductivity of the surface of the toner collecting developer carrier 26, the toner carrier 25 and the toner collecting developer carrier 26, or the toner supplying developer carrier 11 and the toner are adjusted. The effect of preventing leakage between the collecting developer carrier 26 is also obtained.

<Configuration of toner carrier>
The toner carrier 25 is disposed so as to face the toner supply developer carrier 11, the toner collection developer carrier 26, and the image carrier 1, and develops the electrostatic latent image on the image carrier 1. A developing bias is applied by a toner carrier bias power source 31.

  The toner carrier 25 may be made of any material as long as the voltage can be applied, and examples thereof include an aluminum roller that has been subjected to a surface treatment such as alumite. In addition, on a conductive substrate such as aluminum, for example, polyester resin, polycarbonate resin, acrylic resin, polyethylene resin, polypropylene resin, urethane resin, polyamide resin, polyimide resin, porsulfone resin, polyether ketone resin, vinyl chloride resin, vinyl acetate You may use what gave resin coatings, such as resin, a silicone resin, a fluororesin, and rubber coatings, such as silicone rubber, urethane rubber, nitrile rubber, natural rubber, and isoprene rubber. The coating material is not limited to this.

  Further, a conductive agent may be added to the bulk or surface of the coating. Examples of the conductive agent include an electronic conductive agent or an ionic conductive agent. Examples of the electronic conductive agent include carbon black such as kettin black, acetylene black, and furnace black, metal powder, and metal oxide fine particles, but are not limited thereto. Examples of the ionic conductive agent include cationic compounds such as quaternary ammonium salts, amphoteric compounds, and other ionic polymer materials, but they are not particularly limited. Furthermore, a conductive roller made of a metal material such as aluminum may be used.

<Operation of the device>
An example of the operation of the developing device 2a will be described in detail with reference to FIG.

  The developer 24 in the developer tank 16 is mixed and stirred by the rotation of the mixing and stirring members 17 and 18 and is frictionally charged. At the same time, the developer 24 is circulated and conveyed in the developer tank 16 to the sleeve roller 12 on the surface of the developer carrier 11. Supplied.

  The developer 24 is held on the surface side of the sleeve roller 12 by the magnetic force of the magnet body 13 inside the toner supply developer carrier 11 and rotates together with the sleeve roller 12 to be transferred to the toner supply developer carrier 11. The amount of passage is regulated by the regulating member 15 provided to face.

  Thereafter, the developer 24 is conveyed to the toner supply area 7 facing the toner carrier 25.

  In the toner supply region 7, developer spikes are formed by the magnetic force of the main magnetic pole N <b> 1 of the magnet body 13, and due to the development bias applied to the toner carrier 25 and the toner supply bias applied to the toner supply developer carrier 11. The toner in the developer 24 is supplied to the toner carrier 25 side by the force applied to the toner by the formed electric field.

  Usually, a bias in which an AC voltage is superimposed on a DC voltage is applied to the toner carrier 25, and a bias in which only a DC voltage or an AC voltage is superimposed on a DC voltage is applied to the developer carrier 11 for supplying toner. In the supply region 7, an electric field in which an alternating electric field is superimposed on a DC electric field is formed as a supply electric field.

  The toner layer supplied to the toner carrier 25 by the supplied electric field is conveyed to the developing region 6 as the toner carrier 25 rotates, and is formed by the developing bias and the latent image potential on the image carrier 1. The latent image is developed into a visible image by the developing electric field. The development method may be a reversal development method or a regular development method.

  The toner layer (development residual toner) that has consumed toner in the development area 6 is further conveyed to the toner collection area 8 facing the toner collection developer carrier 26.

  On the other hand, the remaining developer 24 that has supplied the toner to the toner carrier 25 in the toner supply region 7 is conveyed to a portion facing the developer carrier 26 for collecting the toner, and the magnetic pole of the developer carrier 11 for toner supply is conveyed. The toner is transferred to the toner collecting developer carrier 26 by the magnetic field formed by S1 and the magnetic pole N4 of the toner collecting developer carrier 26.

  The developer 24 delivered to the toner collecting developer carrier 26 rotates and moves together with the sleeve roller 27 of the toner collecting developer carrier 26 and is conveyed to the toner collecting region 8 facing the toner carrier 25. The

  In the toner collection area 8, developer spikes are formed by the magnetic force of the main magnetic pole S 3 of the magnet body 28, and the development bias applied to the toner carrier 25 and the toner collection bias applied to the toner collection developer carrier 26. Due to the force applied to the toner by the formed electric field, the development residual toner on the toner carrier 25 is collected to the toner collecting developer carrier 26 side.

  Usually, a bias obtained by superimposing an AC voltage on a DC voltage is applied to the toner carrier 25, and a bias obtained by superimposing an AC voltage on the DC voltage alone or a DC voltage is applied to the developer carrier 26 for collecting toner. Similarly to the toner supply area 7, an electric field in which an alternating electric field is superimposed on a DC electric field is formed as a recovery electric field in the toner recovery area 8.

  The toner collection bias is set so that the average value of the applied voltages of the toner carrier 25 and the toner collection developer carrier 26 satisfies the following condition. That is, an electric field is formed in such a direction that the toner on the toner carrier 25 receives a force in a direction toward the toner collecting developer carrier 26.

  As a result, the residual toner on the toner carrier 25 is recovered by the developer on the toner recovery developer carrier 26.

  In the above, the average value of the applied voltage is a voltage value in the case of a DC bias, and a DC component value in the case of an AC superimposed bias. For example, in the case of an asymmetric wave system such as a rectangular wave having a duty ratio, it is a time average. It is.

  The developer 24 containing the toner collected on the toner collecting developer carrier 26 is conveyed toward the developer tank 16 along with the rotation of the sleeve 27, and is generated by the repulsive magnetic fields of the same pole portions N 6 and N 4 of the magnet body 28. The toner is separated from the toner carrier 26 on N6 and collected into the developer tank 16.

  When a supply control unit (not shown) provided in the supply unit 10 detects from the output value of the ATDC sensor 20 that the toner density in the developer 24 has become equal to or lower than the minimum toner density for securing the image density, it is not shown. The replenishment toner 23 stored in the hopper by the toner replenishing means is supplied into the developer tank 16 via the toner replenishing unit 10.

(Problems in the toner collection area and the mechanism of charge removal from adhered toner)
Toner recovery capability in the toner recovery area, the toner accumulation on the surface of the toner recovery developer carrier that causes the problem, and the toner on the surface of the toner recovery developer carrier to suppress it. A mechanism that is made of a material having such a charged series polarity and that neutralizes the surface-attached toner will be described.

  Hereinafter, first, the problem of toner recovery capability will be described by taking as an example a case where the polarity on the charging series in which the material on the surface of the developer carrying member for toner recovery does not take charge of the toner is considered.

<Bias setting and toner collection>
In the toner collection area 8, a development bias is applied to the toner carrier 25, and a toner collection bias is applied to the toner collection developer carrier 26 to form a collection electric field. By this recovery electric field, the development residual toner moves from the toner carrier 25 to the developer carrier for toner recovery and is recovered.

  When the voltage applied to the toner carrier 25 is on the same polarity side as the toner in the relative relationship with the voltage applied to the toner collection developer carrier 26, that is, the toner is directed toward the toner collection developer carrier 26. When a bias in the attracting direction is applied, naturally the force collected from the toner carrier 25 toward the toner carrier 26 is applied to the toner collection region 8.

  However, even when this relationship is in the opposite direction or when both are set to the same potential, the development residual toner can be collected. This is because the surface potential of the toner carrier 25, which is the voltage applied to the toner carrier 25 plus the potential of the undeveloped toner after non-image area development, is relative to the voltage applied to the developer carrier 26 for toner recovery. This is the case where the toner has the same polarity as the toner.

  In this case, an electric field is formed in the toner collection area 8 in a direction in which the toner on the toner carrier 25 is collected toward the toner collection developer carrier 26, and the development residual toner is collected.

  In the case where an AC voltage is included in the voltage applied to the toner carrier 25 or the toner collection developer carrier 26, the relative relationship of the voltages is compared with the average potential of one cycle as a reference, so that the toner collection region 8 Whether or not a recovery electric field is formed can be determined.

<Lower toner accumulation and recovery capability>
In the toner collection area 8, the toner is collected by the collection electric field as described above, and at the same time, the collection electric field is also formed in the developer conveyed on the surface of the toner collecting developer carrier 26 by this electric field. . This electric field adheres to the carrier and gives the toner in the direction of moving to the surface of the toner collecting developer carrier 26 also to the toner being conveyed.

  In other words, when this recovery electric field is strong, the toner in the developer (rising) is separated from the carrier in the toner recovery area 8, the toner moves to the surface of the toner recovery developer carrier 26, and the uneven distribution of the toner on the surface. It happens to happen.

  In this state where the toner is unevenly distributed on the surface, as described above, when the developer 24 is once removed from the toner collecting developer carrier 26, the unevenly distributed toner remains as it is on the surface of the toner collecting developer carrier 26. To remain. As a result, accumulation of toner occurs on the toner collecting developer carrier 26 by repeated use.

  Accumulation of charged toner obstructs the recovery electric field in the toner recovery area 8 and lowers the toner recovery capability. For this reason, the ability to collect the development residual toner does not last for a long time, and ghosting becomes a problem as image formation is repeated.

  In the present embodiment, in order to prevent uneven distribution of toner on the surface of the toner collecting developer carrier 26 due to the collecting electric field in the toner collecting region 8, the surface of the toner collecting developer carrier 26 is made conductive. And a material that neutralizes the toner by contact charging with the toner adhering to the surface.

<Functional operation of contact between static eliminating material and toner>
Hereinafter, the description will return to the example of the developing device 2a according to the present invention in which the material on the surface of the developer carrying member for collecting toner has conductivity and has a polarity on the charging series so as to remove the toner contacted on the surface. The static elimination mechanism will be described.

  The developer 24 that has passed through the toner collection area is conveyed toward the developer tank 16 along with the rotation of the sleeve 27, and the toner collection developer is carried on N 6 by the repulsive magnetic fields of the same-polarity portions N 6 and N 4 of the magnet body 28. It is peeled off from the body 26 and collected into the developer tank 16.

  At this time, the toner mixed in the carrier in the developer is peeled off from the sleeve roller, but the toner that is unevenly distributed on the surface of the sleeve roller is electrostatically attached. Not.

  In the case of the conventional method in which the material on the surface of the developer carrying member 26 for collecting the toner does not take into account the polarity on the charging series that neutralizes the toner, the toner accumulates the adhesion amount every rotation without leaving the surface. As a result, a thick toner layer is formed, and the surface potential of the toner collecting developer carrier 26 is increased.

  This hinders the recovery electric field in the toner recovery area 8 and has an adverse effect on the toner recovery. For this reason, the recoverability that was initially sufficient does not last for a long period of time, and eventually ghosts are generated as image formation is repeated.

  In the present embodiment, the surface of the developer carrying member 26 for collecting the toner is composed of a material 41 that has conductivity and has a polarity on the charging series that neutralizes the toner that contacts the surface. Therefore, the toner that is unevenly distributed on the surface of the toner collecting developer carrier 26 is neutralized by frictional resistance against the surface during rotation of the sleeve roller 27, and the electrostatic adhesion force is remarkably reduced, so that the carrier that conveys the surface is removed. Captured inside.

  As a result, even if the toner is temporarily unevenly distributed in the recovery electric field of the toner recovery area 8, it does not accumulate for a long time until it adversely affects the recovery of the development residual toner.

  As a result, the toner recovery capability of the toner recovery developer carrier 26 is maintained over a long period of time, and the development residual toner can be reliably recovered. As a result, it is possible to provide a high-quality developing device and image forming apparatus that do not generate ghosts.

(Second Embodiment)
Next, a second embodiment of the present invention will be described below with reference to the drawings. The image forming apparatus according to the second embodiment is different from the first embodiment only in the developing device.

(Configuration and operation of developing device 2b)
FIG. 2 shows a configuration example of main parts of an image forming apparatus and a developing device according to the second embodiment of the present invention. With reference to FIG. 2, a configuration and an operation example of the developing device 2b according to the second embodiment will be described.

  In FIG. 2, members having the same functions as those in FIG. 1 are denoted by the same reference numerals as those in FIG. Only differences from FIG. 1 (first embodiment) will be described.

  In the developing device 2b, the surface of the developer carrying member 26 (the surface of the sleeve roller 27) for collecting the toner is made of a charge-removing material 41 that is conductive and has a polarity that removes the toner on the charging series. The following developer disturbing member 42 is provided.

  That is, the toner collection developer carrier 26 is conveyed to the surface of the sleeve roller 27 at a position downstream of the portion facing the toner carrier 25 and upstream of the same polarity portions N4 and N6 with respect to the rotation direction of the toner collecting developer carrier 26. A developer disturbing member 42 is provided so as to come into contact with the developer 24 that is being used.

  The developer disturbing member 42 is in contact with the developer 24 being conveyed with a pressure contact force that does not block the conveyance of the developer 24. By applying pressure to the developer 24, the unevenly distributed toner and toner underneath The contact of the surface of the collecting developer carrying member 26 (the surface of the sleeve roller 27) with the charge eliminating material 41 is promoted. As a result, a higher charge removal effect can be obtained, and for example, even when the charge amount of the toner is increased in a low temperature and low humidity environment, the unevenly distributed toner can be reliably eliminated.

  The developer disturbing member 42 is effective only by urging the contact between the unevenly distributed toner and the charge removing material 41 on the surface of the toner collecting developer carrier 26 by pressure, but at least the surface is made conductive and the developer disturbing member 42. If a bias is applied between the toner collecting developer carrier 26 and the developer collecting member 26 to apply a force in the direction of moving the normally charged toner toward the developer disturbing member 42, the unevenly distributed toner is more effectively eliminated, which is preferable. .

  In this case, the bias is effective if the direction of the electric field is as described above, and may be a DC voltage or an AC voltage. The direction of the electric field in the case of an AC voltage is the direction of the electric field defined by the relative relationship between the average values of the applied voltages of the developer disturbing member 42 and the toner collecting developer carrier 26.

  The average value of the applied voltage is a voltage value in the case of a DC bias, and a DC component value in the case of an AC superimposed bias. For example, in the case of an asymmetric wave system such as a rectangular wave having a duty ratio, it is a time average. .

  Further, when a bias is applied so as to have the electric field direction as described above, a force in a direction to move the normally charged toner toward the developer disturbing member 42 acts, so that the toner in the developer 24 moves due to the electric field. In some cases, the developer disturbing member 42 is unevenly distributed on the surface.

  Since this unevenly distributed toner generates a surface potential in the direction of canceling the bias on the surface of the developer disturbing member 42, there is a fear that the effect of eliminating the unevenly distributed toner on the surface of the developer collecting member 26 for collecting toner by the applied bias may be reduced.

  In order to avoid this, the surface of the developer disturbing member 42 has conductivity as well as the surface of the developer carrying member 26 for collecting the toner so that the toner is neutralized on the charging series. It is good to comprise with the static elimination material 41 of a right polarity.

  As a result, the toner unevenly distributed on the surface of the developer disturbing member 42 is neutralized and taken into the developer 24 being conveyed, and accumulation of unevenly distributed toner does not occur on the surface of the developer disturbing member 42, so that the effect of the bias is maintained. .

  As a material constituting the surface of the developer disturbing member 42 at this time, the same material as the charge eliminating material 41 constituting the surface of the toner collecting developer carrier 26 can be used.

  Further, the form of pressure contact of the developer disturbing member 42 at this time is not particularly limited as long as it is a form in contact with the developer 24 on the toner collecting developer carrier 26 with an appropriate pressure. For example, FIG. Various forms are possible as shown in (a) to (f).

  FIG. 3A shows a form in which a flexible film-like developer disturbing member 42 is cantilevered and is brought into contact with the developer 24 by utilizing the elasticity of the film.

  FIG. 3 (b) shows a film developer disturbing member 42 which is also flexible and is in contact with the developer 24 while supporting only the both ends and stretching the vicinity of the contact portion in an arc shape. It is.

  FIG. 3C shows the developer disturbing member 42 pressed from the back surface by the elastic member 43 and brought into contact therewith. Examples of the elastic member 43 to be used include foamed urethane foam.

  FIG. 3D shows a developer disturbing member 42 in which the surface of a roller made of metal or the like is coated with a material for discharging the toner and is in contact with the developer carrying member 26 for collecting the toner.

  FIG. 3 (e) similarly uses a roller-like developer disturbing member 42. The difference from FIG. 3 (d) is that an elastic layer is provided on the roller.

  In FIG. 3F, a material for discharging the toner is coated on the free end side of a plate spring such as a metal that is cantilevered, and the portion is brought into contact with the developer 24.

  As mentioned above, although illustrated as a form of the developer disturbance member 42, it is not limited to the form quoted here.

  The result of having carried out in order to confirm an effect using the developing device concerning the embodiment mentioned above is described. The experiment was carried out in an NN environment (23 ° C. and 65% RH) and an LL environment (10 ° C. and 15% RH).

  As the developing device used, a developing device having a configuration corresponding to the developing devices 2a and 2b was prepared.

  As the image forming apparatus, a bizhub C350, which is an MFP manufactured by Konica Minolta Business Technologies, Inc., was modified and used with the developing device 2a or 2b having the configuration shown in FIG. The developer for bizhub C350 was also used as the developer. The polarity of the toner was negatively charged, and the toner concentration of the developer was 8%.

  In each developing device, the development gap between the image carrier and the toner carrier was 0.15 mm. The toner supply gap between the toner carrier and the toner supply developer carrier, the toner collection gap between the toner carrier and the toner collection developer carrier, and the gap between the toner supply developer carrier and the regulating member are 0 respectively. .35 mm.

  The voltage applied to the toner carrier was a rectangular wave voltage with an amplitude of peak to peak of 1.4 kV, a DC component of −300 V, a frequency of 4 kHz, and a duty ratio of 50%.

The voltage applied to the developer carrier for supplying toner was DC-550V in the NN environment and DC-650V in the LL environment. At this time, the amount of the toner layer on the toner carrier was 5 g / m ² in any environment. The voltage applied to the developer carrying member for collecting toner was set to DC-100V regardless of the environment.

  The background portion potential of the electrostatic latent image formed on the image carrier was adjusted to be −550V, and the image portion potential was adjusted to −60V.

  In the examples and comparative examples described later, the image chart showing the output image in FIG. 4 is displayed in the NN environment (23 ° C. 65% RH) and the LL environment (10 ° C. 15% RH) using the above-described image forming apparatus. In both cases, 1000 sheets were continuously printed, and the development history (ghost) occurrence state according to the number of printed sheets was compared.

  An output image 54 in FIG. 4 shows an example in which a ghost has occurred, and a region 54 thinner than the half image portion 53 is generated at a position of the black solid portion 52 after one cycle of the toner carrier. The occurrence of ghost was evaluated by measuring the density of the region 54 corresponding to the black solid portion 52 and the half image portion 53 corresponding to the white solid portion 51 as the background.

  The development history (ghost) was evaluated by a densitometer (X-Rite 310 manufactured by X-Rite). The density of the areas (55a and 55b) respectively corresponding to the black solid part 52 of the printed half image part and the white part 51 as the background is measured. A case where the difference in density was more than 0.05 and 0.1 or less was evaluated as Δ (good), and other cases were evaluated as x (occurrence).

  Also, in order to check whether toner has accumulated on the surface of the developer collecting carrier for collecting toner based on the printing history, the developer is taken out according to the number of printed sheets, and is not separated with the carrier, but is separated from the same polarity part (from the N4 pole). The surface potential (toner layer potential) of the toner layer (unevenly distributed toner) adhering to the surface was measured between the N6 poles).

  When measuring the surface potential, the surface potential meter Model 344 manufactured by TREK was used, and the measurement was performed with the developer carrying member for collecting toner grounded. In the evaluation, if the absolute value of the measured toner layer potential is 50 V or less, it is judged as a level that does not impair the recoverability of the residual toner after development, and is set as ○ (particularly good: 30 V or less) or Δ (good: 50 V or less). If it was above, it judged that it was the level which inhibits, and was set as x (defect).

<Example 1>
The developing device 2a shown in FIG. 1 was used, and a Mag roller having a surface coated with a material in which carbon was dispersed in PTFE was used as a developer collecting member for collecting toner, as a material for neutralizing negative toner.

<Example 2>
A developing device 2b shown in FIG. 2 was used, and a Mag roller having a surface coated with a material in which carbon was dispersed in PTFE was used as the developer carrying member for collecting toner, as in Example 1. As the developer disturbing member, a 80 μm thick film composed of a material in which carbon is dispersed in PTFE was cantilevered in the form shown in FIG. 3A and brought into contact with the developer.

  A rectangular wave voltage having an amplitude of 1.0 kV, a DC component +200 V, a frequency of 4 kHz, and a duty ratio of 50% was applied to the developer disturbing member by a high voltage power source (not shown).

<Comparative example>
As a difference from the developing device 2a of Example 1, a developing device using a Mag roller having no surface coating applied to the surface of the developer carrying member for collecting toner in Example 1 was used. No developer disturbing member was installed.

(Evaluation results)
Table 1 shows the evaluation results of Examples 1 and 2 and Comparative Example.

  In the table, “development history” is an evaluation based on the above-mentioned criteria for determining the ghost occurrence status, and is evaluated by the number of printed sheets of 1000 sheets.

  The “toner layer potential” is an evaluation based on the above-mentioned criteria, which is a result of measuring the surface potential between the N4 and N6 poles on the surface of the developer carrying member for collecting toner. is doing.

  As is apparent from Table 1 by comparing the results of the example of the present invention and the comparative example, in the comparative example, both the NN environment (23 ° C. and 65% RH) and the LL environment (10 ° C. and 15% RH) are used for toner recovery. The toner is unevenly distributed on the surface of the developer carrying member (toner layer potential ×), and the development history is generated (ghost evaluation ×).

  In contrast, in the NN environment of Example 1, neither toner uneven distribution (toner layer potential ◯) nor development history occurred on the surface of the developer carrying member for collecting toner (ghost evaluation ◯). Further, even in the LL environment, the toner is unevenly distributed on the surface of the developer carrying member for collecting toner (toner layer potential Δ), and although the recoverability is slightly reduced, the development history is at an acceptable level in image quality (ghost evaluation Δ). there were.

  Further, in Example 2 in which the developer disturbing member is installed, neither the NN environment nor the LL environment causes the toner uneven distribution (toner layer potential ◯) or the development history on the surface of the toner collecting developer carrier (ghost). Evaluation ○).

  That is, compared to the comparative example, in Examples 1 and 2, the recovery of the development residual toner on the toner carrier can be stabilized, and a good image output can be stably obtained regardless of the use environment. is there.

  As described above, according to the developing device and the image forming apparatus according to the present embodiment, the toner collection developer carrying member reliably collects the development residual toner on the toner carrying member, and the toner collecting developer carrying member. Since accumulation of toner on the body can be avoided, a stable toner layer is always supplied onto the toner carrier. As a result, it is possible to obtain a high-quality image over a long period of time, in which the toner recovery capability is maintained and the ghost problem does not occur.

  In addition, the above-mentioned embodiment is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a cross-sectional view illustrating a configuration example of a main part of a developing device 2a according to a first embodiment and an image forming apparatus including the same. It is sectional drawing which shows the structural example of the principal part of the developing device 2b which concerns on 2nd Embodiment, and an image forming apparatus provided with the same. It is sectional drawing which shows each form example of the developer disturbance member in the image development apparatus 2b. It is a figure which shows the example of an output of the image for evaluation of a development history (ghost).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image carrier 2a, 2b Developing device 3 Charging member 4 Transfer roller 5 Cleaning blade 6 Development area 7 Toner supply area 8 Toner collection area 11 Toner supply developer carrier 12 Sleeve roller 13 Magnet body 16 Developer tank 24 Developer 25 Toner carrier 26 Toner collection developer carrier 27 Sleeve roller 28 Magnet body 41 Static eliminating material 42 Developer disturbing member

Claims (7)

A developer tank containing a developer including toner and a carrier;
A toner carrying developer carrier for carrying and feeding the developer supplied from the developer tank;
A toner carrier that receives and supplies the toner from the toner supply developer carrier and develops a latent image on the image carrier;
A developing device comprising: a toner collecting developer carrier that carries and conveys the developer and collects development residual toner from the toner carrier;
The toner collecting developer carrier has a conductive surface and is made of a material that discharges the toner by contact charging with the toner adhering to the surface. apparatus. The toner collecting developer carrier is
A sleeve roller having a coating layer made of a material that is rotatable in the circumferential direction, has a conductivity on the surface, and removes the toner by contact charging;
The developing device according to claim 1, further comprising: a magnet body included in the sleeve roller. 3. The developer disturbing member according to claim 1, further comprising a developer disturbing member that comes into contact with the developer collecting member for collecting toner via a developer layer collected with toner on the developer collecting member for collecting toner. Development device. The developing device according to claim 3, wherein at least a surface of the developer disturbing member has conductivity. The bias voltage in a direction for attracting toner toward the developer disturbing member is applied between the developer disturbing member and the developer carrying member for collecting toner. Development device. The developing device according to claim 3, wherein a surface of the developer disturbing member is made of a material that neutralizes toner by contact charging. An image carrier and a developing device for developing a latent image formed on the surface of the image carrier to form a toner image;
The image forming apparatus according to claim 1, wherein the developing device is the developing device according to claim 1.

Images